The present invention relates in general to mechanisms for providing controllable angular orientation between an outer tubular element and a coaxial inner tubular element while transmitting torsional load between the outer and inner tubular elements. More particularly, the invention is directed to such mechanisms which can be incorporated in a downhole tool coupled within a drill string in a wellbore to provide controllable angular orientation between the sections of the string above and below the tool, while the mechanism is subjected to torsional load.
In drilling a borehole (or wellbore) into the earth, such as for the recovery of hydrocarbons or minerals from a subsurface formation, it is conventional practice to connect a drill bit onto the lower end of a “drill string”, then rotate the drill string so that the drill bit progresses downward into the earth to create the desired borehole. A typical drill string is made up from an assembly of drill pipe sections connected end-to-end, plus a “bottomhole assembly” (“BHA”) disposed between the bottom of the drill pipe sections and the drill bit. The BHA is typically made up of sub-components such as drill collars, stabilizers, reamers and/or other drilling tools and accessories, selected to suit the particular requirements of the well being drilled.
In conventional vertical borehole drilling operations, the drill string and bit are rotated by means of either a “rotary table” or a “top drive” associated with a drilling rig erected at the ground surface over the borehole (or in offshore drilling operations, on a seabed-supported drilling platform or suitably-adapted floating vessel). During the drilling process, a drilling fluid (commonly referred to as “drilling mud” or simply “mud”) is pumped under pressure downward from the surface through the drill string, out the drill bit into the wellbore, and then upward back to the surface through the annulus between the drill string and the wellbore. The drilling fluid carries borehole cuttings to the surface, cools the drill bit, and forms a protective cake on the borehole wall (to stabilize and seal the borehole wall), in addition to other beneficial functions.
As an alternative to rotation by a rotary table or a top drive, a drill bit can also be rotated using a “mud motor” (alternatively referred to as a “downhole motor”) incorporated into the drill string immediately above the drill bit. The mud motor is powered by drilling mud pumped under pressure through the mud motor in accordance with well-known technologies. The technique of drilling by rotating the drill bit with a mud motor without rotating the drill string is commonly referred to as “slide” drilling, because the non-rotating drill string slides downward within the wellbore as the rotating drill bit cuts deeper into the formation. Torque loads from the mud motor are reacted by opposite torsional loadings transferred to the drill string.
Directional drilling operations using a mud motor require means for controlling the orientation of the mud motor relative to earth while the motor is down hole, in order to control the resulting direction of the curved or deflected wellbore. When drilling with a conventional string of drill pipe, mud motor orientation control can be accomplished by rotating the entire pipe string from surface. However, when drilling with coiled tubing, which cannot easily be rotated from surface, orientation control must be accomplished using means capable of controlling the angular orientation of the mud motor relative to the coiled tubing. It is desirable for this relative orientation to be controllable while drilling operations are in progress, to avoid any unexpected and undesired changes in orientation due to the unwinding and recoiling of the coiled tubing that can occur when drilling is interrupted.
Previous devices typically include an arrangement of lugs and spiral grooves, or an arrangement of lugs and circumferentially-spaced cam bodies, that convert axial motion of a piston into rotational motion of the lower string components. Such devices are generally very complicated in construction and operation, with large numbers of components. The devices also do not allow orientation to be controlled and adjusted while being subjected to torsional loads (such as under normal drilling conditions).
Accordingly, there remains a need for improved and less complicated apparatus for controlling and adjusting the angular orientation between coaxial tubular elements, particularly while under torsional loading. The present invention is directed to this need.